1. Field of the Invention
This invention relates to devices for reducing air flow resistance and drag on trucks, semitrailers, and other vehicles, and, more particularly, to devices for introducing air from airstreams passing around the vehicle into drag creating volumes at the rear of the vehicle, beneath such vehicle, and between units of a combination vehicle.
2. Description of the Prior Art
Fuel conservation and the operational economies associated therewith have become increasingly important, particularly to businesses involved in long distance highway cargo transport. Heretofore, most designers attempting to improve fuel utilization efficiency have addressed reduction of resistance of the vehicle to passage through the air. However some efforts have been directed toward reduction of drag.
As a vehicle progresses along its path, the volume of air immediately in front of the vehicle acts as a barrier, reducing fuel economy. Significant advances have been made in aerodynamic design of semitrailer tractors, including the incorporation of deflectors. Some of these deflectors even provide for deflection of air over or around a substantially vertical planar front surface of a trailer body. Additionally, cone-shaped appliances have been constructed for attachment to the front surface of a trailer body to aid in deflecting air around the trailer. An elementary version of an airstream deflector is described in U.S. Pat. No. 4,159,845 to Bratsberg.
In addition to air flow resistance, fuel economy is adversely affected by drag caused by the creation of volumes of air having a reduced pressure, primarily at the rear of the vehicle, among irregular structure under the vehicle, and between units of a combination vehicle. Considering the rear of the vehicle, the airstreams passing over the top of the vehicle and along its sides tends to attempt to enter the volume immediately to the rear of the rear surface of the vehicle, but is impeded in so moving by turbulance caused by the passage of the vehicle. Thus, the vehicle is, in effect, pulling this turbulent volume along with its passage. Several alternate methods of eliminating this volume of turbulent, drag inducing air are taught in the prior art. A first approach is to deflect a portion of the airstreams passing along the sides of the vehicle into a flow path substantially parallel to the rear surface of the vehicle, as described in U.S. Pat. No. 3,072,431 to Schumaker, U.S. Pat. No. 3,960,402 to Keck, U.S. Pat. No. 4,214,787 to Chain, or U.S. Pat. No. 4,433,865 to Crompton, Jr. Schumaker employs a pair of arcuate deflector vanes attached vertically to rear vertical corner edges of the trailer, the attachment providing that a portion of each vane projects into the air stream passing along the sides of the vehicle, within state and federal width restrictions, to capture a portion of the air flow and deflect to into the drag volume region. Keck adds a horizontal vane attached along the top rear corner edge so as to downwardly deflect a portion of the air flowing along the top surface of the trailer into the drag volume region. Chain adds hydraulic actuators to the vane so that either flat or arcuate vanes may be varied in their angular positions to vary the volume of air deflected into the drag region. Crompton, Jr., while not specifically addressing deflection of air for the purpose of drag reduction, utilizes vertical vanes that are coupled together in a manner such that when one vane is deflected toward a longitudinal vehicle center line, the other vane is caused to move outwardly from that center line. When both vanes are in their rest position, their trailing edges project slightly outwardly away from the center line. The passage of another vehicle, usually in an opposed direction, causes the rear of the trailer to sway from buffeting by the air stream of the passing vehicle. The vane on that side of the vehicle is then deflected inwardly, with its coupled mate being moved outwardly further into the air stream along the other side of the vehicle, which sets up a countering force to overcome the sway tendency. Unless care is taken in the design of the vanes of Crompton, Jr., the vanes may provide an increased drag volume region at the rear of the vehicle.
A second approach to drag reduction appearing in the prior art can be categorized as structurally altering the shape of the rear of the vehicle to form a boat tail structure which aids in allowing a generally laminar air flow along such extended structure, thus removing the turbulent drag inducing volume region, as taught by Keedy in U.S. Pat. No. 4,142,755 or Scanlon in U.S. Pat. No. 4,818,015.
Since even minor reductions in wind flow resistance and drag can result in significant economic savings over long distance vehicle operations, the prior art has addressed drag reduction between units of a combination vehicle and some consideration has been given to air flow problems arising beneath the vehicle. Some prior art has provided skirts to cover gaps between a tractor unit and its trailer, as well as skirts depending toward the roadway to partially enclose the undercarriage. U.S. Pat. No. 4,611,847 to Sullivan describes downwardly extendable, inflatable side skirts to help guide air along the external sides of the vehicle combination and to attempt to channel air flowing under the vehicle into a generally forward to rear path. U.S. Pat. No. 4,746,160 to Weisemeyer combines these features with vehicle streamlining and the use of deflectors.
Since the undercarriage of a trailer usually includes transverse chassis beams, axles, landing gear, equipment storage, and other irregular elements, earlier efforts in this area have been minimal, other than with the side skirts mentioned above. However, U.S. Pat. No. 1,726,158 to Masury, et.al., teaches suspending a magnet transverse to the vehicle path in front of the tires and in proximity to the roadway such that the magnet will pick up nails and other magnetic material that may puncture the tires. Subsequently, Thompson, in U.S. Pat. No. 3,874,697, considers the adverse effects of water and other materials that are picked up by the tires and carried therealong to be expelled in a generally forward direction near the top of revolution of the tire. Thompson thus adds a deflector shield, in the form of an arcuate, channeled panel, which is disposed across the underside of the vehicle longitudinally adjacent the wheels to deflect water, snow, and air flow downwardly rather than in opposition to vehicle travel. Fitzgerald, et.al., in U.S. Pat. No. 4,640,541, describes a device placed transversely between tandem rear axles and wheels which directs air flow, water, snow, and the like laterally downwardly toward the space transversely between opposed wheels of a single axle. Grooves or channels in an arcuate surface of the device are used to accomplish this deflection.
Based on the above, no single reference appears to address all aspects of air resistance and drag reduction, even though most of the more important causes of reduced fuel economy appear to have been given consideration. The sole exception to these factors seems to rest in the area of treatment of the vehicle undercarriage. It should also be noted that the prior art appears limited to addressing situations wherein the air streams around a vehicle are substantially along the direction of its travel. Recent studies indicate that certain of the above-described drag reduction techniques may be of limited usefulness when transverse wind conditions impinge upon the vehicle. Such studies further suggest that drag may even be increased under such conditions. Yet another question of use of such devices arises when loading or unloading of the vehicle is taken into account. Since many cargo vehicles provide access through doors on the rear surface, such devices may interfere with opening and closing the loading doors. Additionally, when the vehicle is backed into some loading dock facilities, the deflector vanes and other such drag reduction devices may be damaged by, or otherwise interfere with, contact with the loading dock structure.